accelerating hard and shift shock, is it unavoidable?

[MJinZ]

Yep, the newest Merc C63 has the dual-clutch MCT7, dropping the torque converter slushbox design. Most Mercedes don't use the MCT7 though.

The BMW autos are still slushboxes, but the M cars have SMGs instead.

As the DCT/SMG design is a rougher, more performance-oriented solution, it doesn't have a place in replacing the conventional auto slushbox design in most passenger cars, particularly in pure luxury models that depend on smoothness/quietness as far more important than shifting in .00x MS.

The M3 does not use the SMGs anymore, hasn't for years.

 

[Ronstang]

I am not reading all of this but if you have a lot of "shock" when you shift at WOT in a manual then you are definitely not doing it right or you have such a crappy shifter that you cannot do it right. You need a good shifter with physical stops that prevent you from bending shift forks and such and you only need to lift the throttle for such a short time that there really should not be much shock. I can throw a shifter so fast in a mustang that you won't feel much. You hear more than you feel. You can do it with any shifter but it is much harder if you have to worry about putting too much pressure on the shifter.

If you have a cable shifter you might as well get used to the shock.

 

[EightySix Four]

you can get a lighter flywheel for improved response, but then you can also stall it easier. Flywheels are supposed to be heavy.

Not 55lbs on a 2l I4 heavy, for example the VW auto group I4 from the B7 A4 uses a 23lb flywheel.

I was thinking about a lighter flywheel for my 8 so it can rev faster, but I also read somewhere that lighter flywheels can decrease torque at lower RPMs? Is that true? This car is pretty torqueless as is already.

An RX-8 does not need to rev faster, it need to actually make power

how many manufacturers do you know that don't optimize clutch/flywheel operation for ease of use?
esp. pedestrian makes like honda and hyundai.

i thought it'd be pretty obvious.

Some manufacturers use a mid weight flywheel and tune the ECU to control how fast the motor can rev.

I am not reading all of this but if you have a lot of "shock" when you shift at WOT in a manual then you are definitely not doing it right or you have such a crappy shifter that you cannot do it right. You need a good shifter with physical stops that prevent you from bending shift forks and such and you only need to lift the throttle for such a short time that there really should not be much shock. I can throw a shifter so fast in a mustang that you won't feel much. You hear more than you feel. You can do it with any shifter but it is much harder if you have to worry about putting too much pressure on the shifter.

If you have a cable shifter you might as well get used to the shock.

If you remain at WOT and shift, foot still on the gas pedal, there will be a shock as the wheels catch up to the motor which is moving faster than the rest of the drive train.

 

[Ronstang]

If you remain at WOT and shift, foot still on the gas pedal, there will be a shock as the wheels catch up to the motor which is moving faster than the rest of the drive train.

People who powershift correctly shift so fast you are not going to get much shock if any, but I was not talking about powershifting. I actually let up on the throttle a little as I am not racing. It is much easier on the transmission and almost as fast as powershifting. You won't feel much either if you are sitting next to me.

 

[PricklyPete]

I thought people called all Automatics slush boxes?

No...slushboxes are generally used to refer to transmissions that have torque converters...where liquid serves as the power conduit...and a buffer from these abrubt shift changes we are referring to.

DCT's can be calibrated to perform abrupt shifts that lose very little power or they can be calibrated to "slip" a little to smooth out the shift (just like you would with a manual). In some cars, this calibration can be done by the driver depended on how they are planning on driving (sport mode vs. comfort mode).

 

[BassBomb]

cvt

 

[EightySix Four]

People who powershift correctly shift so fast you are not going to get much shock if any, but I was not talking about powershifting. I actually let up on the throttle a little as I am not racing. It is much easier on the transmission and almost as fast as powershifting. You won't feel much either if you are sitting next to me.

Unless you have a turbo, then if you don't powershift, you lose quite a bit (considering a race, it's all relative) as the turbo has to spool back up.

cvt

Can't deal with the power levels in performance vehicles, which is why we ignored the first person who mentioned it.

 

[ShawnD1]

I cringe on a hard 1-2 shift on most cars. A bit less when the wheels brake loose which alleviates some of the shock.

Good to know it's not just me who has a hard time doing 1-2. Always feels like I'm destroying the car, so I typically shift into 2 at a low RPM. I'm not racing my car or anything like that; I just really like gunning it when I'm accelerating to highway speed

 

[Eli]

Since when is this feeling a bad thing? It's not a jolt.. it's a pull.

Cringe? Hard time doing 1-2? The hell is wrong with you people?

Perhaps you should all be driving autos.

 

[exdeath]

Close ratio 6 speed T56 + Spec stage 3+ 11" metalic clutch = 2000screeeeeeee6500..shift BANG.screeeee6500... shift CLUNK hophophophopchirp chirp chirp S shape oh hey we're finally moving.

That clutch is fucking brutal on non solid bushings. Can't imagine living with an unsprung clutch disc.

All production cars ship from the factory to please the noise/vibration/harshness (NVH) crowd and create a cushy ride, not stand up to the shock of power shifting.

Thus, if you have excessive bangs and clunks and aren't simply chirping the tires with each shift as the engine grabs the clutch disc and rapes it, then you have loose things moving that shouldn't be, such as play in the differential, axle/driveshaft joints, differential mounts, motor mounts, etc. It should feel like a firm jolt uniformly through the entire car and a light tire chirp as the drive line is suddenly asked to instantly increase by 500+ RPM.

 

[vshah]

... Yes, but if it has a heavy flywheel then you can't "fix" it from software, you have to physically replace the flywheel.

my civic Si has serious rev hang which can be mitigated by a re-flash of the ECU. so for my car at least, it is a ECU/software issue. intentional or not i can't say. it makes it slower to shift at WOT if i want to be nice to the car. especially since its a ~3500 rpm drop shifting at WOT.

If you remain at WOT and shift, foot still on the gas pedal, there will be a shock as the wheels catch up to the motor which is moving faster than the rest of the drive train.

you also may run into the rev limiter/fuel cutoff when shifting at redline, but i agree you'll still feel a shock.

 

[exdeath]

I was thinking about a lighter flywheel for my 8 so it can rev faster, but I also read somewhere that lighter flywheels can decrease torque at lower RPMs? Is that true? This car is pretty torqueless as is already.

Lighter flywheel does not change torque or horsepower. It's a placebo effect in that the engine has an easier time revving up faster and you feel the power sooner, but it's making the same power at that RPM that it was before. The tradeoff is that it's easier to bog/stall at low RPM, especially with an aggressive clutch material.

 

[exdeath]

my civic Si has serious rev hang which can be mitigated by a re-flash of the ECU. so for my car at least, it is a ECU/software issue. intentional or not i can't say. it makes it slower to shift at WOT if i want to be nice to the car. especially since its a ~3500 rpm drop shifting at WOT.

All fuel injection cars have what is called a dashpot function, which controls the idle air valve when the throttle is shut instantly, and how smooth the RPM drops back to idle. That is used to control how lofty or quickly the RPM drops, and is usually matched to the characteristics of the transmission (spread between gears, etc).

 

[vshah]

All fuel injection cars have what is called a dashpot function, which controls the idle air valve when the throttle is shut instantly, and how smooth the RPM drops back to idle. That is used to control how lofty or quickly the RPM drops, and is usually matched to the characteristics of the transmission (spread between gears, etc).

heh, definitely NOT matched well in my car stock. they actually issued a TSB to fix it on 06 models, but left the 07s out. a hondata reflash or tune can reduce the effect though. as it is right now, it hovers for almost a second before dropping. i get around it by letting up on the gas a bit before i open the clutch.

Lighter flywheel does not change torque or horsepower. It's a placebo effect in that the engine has an easier time revving up faster and you feel the power sooner, but it's making the same power at that RPM that it was before. The tradeoff is that it's easier to bog/stall at low RPM, especially with an aggressive clutch material.

shouldn't it have basically the same effect as lighter wheels? reduced rotational mass/lower inertia? (not counting the handling benefits of lighter wheels)

 

[exdeath]

heh, definitely NOT matched well in my car stock. they actually issued a TSB to fix it on 06 models, but left the 07s out. a hondata reflash or tune can reduce the effect though. as it is right now, it hovers for almost a second before dropping. i get around it by letting up on the gas a bit before i open the clutch.

Sounds like TBW teething problems. Using the large slow throttle with TBW to simulate a smaller more accurate IAC.

 

[EightySix Four]

shouldn't it have basically the same effect as lighter wheels? reduced rotational mass/lower inertia? (not counting the handling benefits of lighter wheels)

It's a similar affect but much more pronounced since there is such a large change in the rev characteristics when the clutch is in and you're more likely to stall.

 

[Arkaign]

The M3 does not use the SMGs anymore, hasn't for years.

It's still a computer controlled sequential manual gearbox, but it's now a dual-clutch model, so DCT=SMG

 

[EightySix Four]

It's still a computer controlled sequential manual gearbox, but it's now a dual-clutch model, so DCT=SMG

Meh, we're kinda stretching different terms now to cover our asses, while technically correct, we all know there is a diff between DCT and SMG gear boxes from a BMW perspective

 

[MJinZ]

It's still a computer controlled sequential manual gearbox, but it's now a dual-clutch model, so DCT=SMG

Well SMG is a BMW invention, the M- double clutch DCT's are made by Getrag I believe.

Their differences are substantial enough that you can't really equate a SMG to a DCT. The DCT is also quite a bit superior.

 

[DivideBYZero]

Well SMG is a BMW invention, the M- double clutch DCT's are made by Getrag I believe.

Their differences are substantial enough that you can't really equate a SMG to a DCT. The DCT is also quite a bit superior.

The original SMG units were also Getrag, in fact they were the same Getrag manual transmissions in both SMG and manual equiped cars, except the SMG version was actuated via hydraulics. Now with the DCT the transmission is very different, but it is STILL an SMG. SMG only stands for Sequential Manual Gearbox, which the DCT still is, is does not specify the type of SMG hardware.

 

[Zap]

How well does the "rev matching" work in the 370z?

 

[DivideBYZero]

How well does the "rev matching" work in the 370z?

This is only on down-shifts AFAIK.

 

[reallyscrued]

No, the cars you drove just suck/and or have the transmission suckage.

Please stop posting in The Garage.

 

[Rifter]

It's hard/impossible to shift smothly if you keep your foot on the floor. You can negate this effect by either slipping the clutch or taking your foot off the gas. Depending on the vehicle it can be impossible to shift at WOT with no shock.

The manual vs auto shock totally depends on what transmission you have. I have a Manual and can shift pretty smoothly WOT by slipping the clutch enough, i also have a really light car and light flywheel(88 CRX Si). My brothers car is an auto and will snap you neck at every shift if you are WOT, the only time it doesnt is if when you hit second it breaks the tires loose, this smoothens it out alot but can be dangerous if you are cornering and arnt ready for it, its a 89 5.0 Mustang GT making 330HP, 4 spd auto, shift kit and just rebuilt trans with drag racing in mind, i hate it, my bro loves it.

There are tons of cars that are the other way around where the auto is so smooth you hardly feel it and there are manuals when you cant help a little jerk at WOT.

So the answer is it totaly depends on what car you are driving and the skill of the driver(well skill for manual trans anyways, anybody can drive a auto)

 

[AMCRambler]

He has a history of trolling every thread, including his own.

Like I said before though, you can lessen shift shock if you let off the throttle, drop to the right RPM, get off the clutch, and then hammer it again. You're going to lose time, but it's nicer on the drivetrain. My car has a NLS system in it, so when I shift without letting go of the throttle it opens up the cams and burns a little fuel to keep the turbo spinning mid shift. I can usually let the rear end go shifting into 3rd pretty easy and on the rare occasion it hooks, it feels like you've been rear ended by a freight train.

I love gettin' rear ended by a freight train, lol.